This invention relates generally to refrigerators and, more particularly, to a method and apparatus for controlling refrigeration defrost cycles.
Known frost free refrigerators include a refrigeration defrost system to limit frost buildup on evaporator coils. Conventionally, an electromechanical timer is used to energize a defrost heater after a pre-determined run time of the refrigerator compressor to melt frost buildup on the evaporator coils. To prevent overheating of the freezer compartment during defrost operations when the heater is energized, in at least one type of defrost system the compartment is pre-chilled. After defrost, the compressor is typically run for a predetermined time to lower the evaporator temperature and prevent food spoilage in the refrigerator and/or fresh food compartments of a refrigeration appliance.
Such timer-based defrost systems, however are not as energy efficient as desired. For instance, they tend to operate regardless of whether ice or frost is initially present, and they often pre-chill the freezer compartment regardless of initial compartment temperature. In addition, the defrost heater is typically energized without temperature regulation in the freezer compartment, and the compressor typically runs after a defrost cycle regardless of the compartment temperature. Such open loop defrost control systems, and the accompanying inefficiencies are undesirable in light of increasing energy efficiency requirements.
Recognizing the limitations of such timer-based defrost systems, efforts have been made to provide adaptive defrost systems employing limited feedback, such as door openings and compressor and evaporator conditions, for improved energy efficiency of defrost cycles. As such, unnecessary defrost cycles are avoided and the defrost heater is cycled on and only as necessary, such as until the evaporator reaches a fixed termination temperature. See, for example, U.S. Pat. No. 4,528,821. However, achieving some defrost goals, such as melting all of the frost off of the evaporator, are detrimental to achieving other defrost goals, such as maintaining freezer compartment temperatures at sufficient levels during defrost operations to prevent freezer burn and moisture formation/ice buildup in the freezer compartment. Known defrost systems have not resolved these difficulties in an energy efficient manner.
In one aspect, a method for defrosting an evaporator of a refrigeration sealed system is provided. The system includes a controller operatively coupled to an evaporator fan, a condenser fan and a defrost heater, and the method comprises operating the sealed system until a selected time till defrost interval expires, initiating a defrost cycle when the time till defrost interval expires, and selectively operating the sealed system to raise a temperature of the evaporator while the defrost heater is inactivated.
In another aspect, a method for defrosting an evaporator of a refrigeration sealed system is provided. The system includes at least one refrigeration compartment and a controller operatively coupled to a compressor, an evaporator fan and a condenser fan. The method comprises initiating a defrost cycle, operating the sealed system to prechill the refrigeration compartment, and selectively operating the evaporator fan and the condenser fan to raise a temperature of the evaporator.
In another aspect, a method for defrosting a refrigeration appliance is provided. The appliance includes a freezer compartment and a sealed system including a controller and a compressor, an evaporator, a condenser, an evaporator fan and a condenser fan operatively coupled thereto. The method utilizes a defrost heater, and the method comprises operating the sealed system until a selected time till defrost expires, initiating a defrost cycle when the time till defrost expires, operating the sealed system to prechill the refrigeration compartment, selectively operating the sealed system to raise a temperature of the evaporator, and energizing the defrost heater after selectively operating the sealed system to raise a temperature of the evaporator.
In another aspect, a refrigeration unit is provided. The refrigeration unit comprises a compressor, an evaporator fan, a condenser fan, and a controller operatively coupled to said compressor, said evaporator fan and said condenser fan. The controller is configured to deactivate said compressor and selectively operate at least one of said evaporator fan and said compressor fan to raise a temperature of the evaporator when a defrost cycle is initiated.
In another aspect, a refrigeration unit is provided. The refrigeration unit comprises a compressor, an evaporator, a condenser fan, a defrost heater, and a controller. The controller is operatively coupled to said compressor, said evaporator and said defrost heater, and the controller comprises a defrost timer. The controller is configured to operate said compressor in a normal mode and an abnormal load in response to a value of the defrost timer, and said controller is further configured to selectively operate at least one of said evaporator fan and said condenser fan when said time till defrost expires to raise a temperature of the evaporator before energizing said defrost heater.
In another aspect, a refrigerator is provided. The refrigerator comprises a cabinet defining at least one refrigeration compartment, and a sealed system for cooling said at least one refrigeration compartment. The sealed system comprises an evaporator, a defrost heater; and a controller operatively coupled to said sealed system and to the defrost heater. The controller is configured to adaptively control said defrost heater and said sealed system between normal and abnormal time till time till defrost intervals, and when a time till time till defrost interval has expired, said controller is configured to operate said sealed system to prechill said refrigeration compartment and to thereafter selectively operate said sealed system to raise a temperature of said evaporator without energizing said defrost heater.